camshaft

Abstract

To suppress torque fluctuations of a cam shaft while ensuring the flexibility of valve opening / closing control in an internal combustion engine.SOLUTION: Cam shafts 5 and 6 are equipped with a plurality of cams 51 and 61 separated from each other in an axial direction of the cam shafts. The plurality of cams has an asymmetric lift curve, and is formed so that a peak position of negative cam torque generated by a first cam opening / closing valves 7 and 8 disposed on a first cylinder is included in a phase zone where positive cam torque is generated by a second cam opening / closing a valve disposed on a second cylinder, or is formed so that a peak position of positive cam torque generated by the first cam opening / closing the valve disposed on the first cylinder is included in a phase zone where negative cam torque is generated by the second cam opening / closing the valve disposed on the second cylinder.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a camshaft. [Background technology]

[0002] In an internal combustion engine, valves (intake valves and exhaust valves) are opened and closed by a camshaft, which is rotated by the crankshaft via a transmission such as a timing chain. Positive cam torque is generated during the phase section in which the cam of the camshaft opens the valve, and negative cam torque is generated during the phase section in which the cam of the camshaft closes the valve.

[0003] If the fluctuation in cam torque during camshaft rotation becomes large, the fluctuation in tension applied to the transmission device becomes large, resulting in fluttering of the transmission device and reduced durability.In contrast, in the internal combustion engine described in Patent Document 1, two valve lifts, a main lift and a sub-lift, are performed by a single cam in one cycle, and the camshaft is configured so that the cam torque generated by the main lift is offset by the cam torque in the opposite direction generated by the sub-lift. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-257408 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technique described in Patent Document 1 requires the valve to be opened and closed multiple times in one cycle, which reduces the degree of freedom in valve opening and closing control.

[0006] In view of the above-mentioned problems, an object of the present invention is to suppress torque fluctuations of a camshaft while ensuring a degree of freedom in valve opening and closing control in an internal combustion engine. [Means for solving the problem]

[0007] The gist of the present disclosure is as follows.

[0008] (1) A camshaft in an internal combustion engine that is rotationally driven by a crankshaft via a transmission, the camshaft comprising a plurality of cams spaced apart from one another in the axial direction of the camshaft, the plurality of cams having asymmetric lift curves and configured such that the peak position of negative cam torque generated by a first cam that opens and closes a valve located in a first cylinder is included in a phase interval in which positive cam torque is generated by a second cam that opens and closes a valve located in a second cylinder, or such that the peak position of positive cam torque generated by the first cam that opens and closes a valve located in a first cylinder is included in a phase interval in which negative cam torque is generated by a second cam that opens and closes a valve located in a second cylinder.

[0009] (2) The camshaft described in (1) above, wherein the plurality of cams have asymmetric lift curves in which the maximum lift position is closer to the valve closing completion position than the valve opening start position, and the peak position of the negative cam torque generated by the first cam is included in the phase section in which the positive cam torque is generated by the second cam.

[0010] (3) The camshaft according to (1) or (2) above, wherein the plurality of cams are formed so that the peak position of the negative cam torque generated by the first cam substantially coincides with the peak position of the positive cam torque generated by the second cam. [Effects of the Invention]

[0011] According to the present invention, in an internal combustion engine, it is possible to suppress torque fluctuations of a camshaft while ensuring a degree of freedom in valve opening and closing control. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is a diagram that schematically shows an internal combustion engine provided with a camshaft according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic partial cross-sectional view of an internal combustion engine. [Figure 3] FIG. 3 is a timing chart showing the valve lift amount of the intake valve and the cam torque generated in the intake camshaft. [Figure 4] FIG. 4 is a diagram showing an example of a cam profile of an intake cam. [Figure 5] FIG. 5 is a diagram showing the change over time in cam torque generated by a plurality of intake cams having the cam profile shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, like components are designated by like reference numerals.

[0014] 1 is a diagram schematically illustrating an internal combustion engine 1 provided with a camshaft according to an embodiment of the present invention. The internal combustion engine 1 includes a piston 2, a connecting rod 3, a crankshaft 4, an intake camshaft 5, an exhaust camshaft 6, an intake valve 7, and an exhaust valve 8.

[0015] In this embodiment, the internal combustion engine 1 is an in-line four-cylinder engine, and is formed with four cylinders. A piston 2, two intake valves 7, and two exhaust valves 8 are arranged in each cylinder, and a combustion chamber 9 is formed above the piston 2. The piston 2 is connected to a crankshaft 4 via a connecting rod 3. Combustion of an air-fuel mixture in the combustion chamber 9 causes the piston 2 to reciprocate in the axial direction of the cylinder, and the reciprocating motion of the piston 2 is converted into rotational motion of the crankshaft 4 by the connecting rod 3.

[0016] An intake side timing sprocket 10 is provided at one end of the intake camshaft 5, and the intake side timing sprocket 10 is connected to a timing sprocket 13 provided on the crankshaft 4 via a timing chain 12. The timing sprocket 13, timing chain 12, and intake side timing sprocket 10 function as a transmission device that transmits the rotational motion of the crankshaft 4 to the intake camshaft 5. The intake camshaft 5 is rotationally driven by the crankshaft 4 via these transmission devices.

[0017] An exhaust-side timing sprocket 11 is provided at one end of the exhaust camshaft 6, and the exhaust-side timing sprocket 11 is connected to a timing sprocket 13 via a timing chain 12. The timing sprocket 13, timing chain 12, and exhaust-side timing sprocket 11 function as a transmission device that transmits the rotational motion of the crankshaft 4 to the exhaust camshaft 6. The exhaust camshaft 6 is rotated by the crankshaft 4 via these transmission devices. Note that the internal combustion engine 1 may be equipped with a timing belt instead of the timing chain 12 as the transmission device.

[0018] The intake camshaft 5 is provided with multiple intake cams 51 spaced apart from one another in the axial direction of the intake camshaft 5. In this embodiment, eight intake cams 51 are provided on the intake camshaft 5 to open and close a total of eight intake valves 7 arranged in four cylinders. Two intake cams 51 arranged above two intake valves 7 arranged in the first cylinder simultaneously open and close the two intake valves 7 in the first cylinder. Two intake cams 51 arranged above two intake valves 7 arranged in the second cylinder simultaneously open and close the two intake valves 7 in the second cylinder. Two intake cams 51 arranged above two intake valves 7 arranged in the third cylinder simultaneously open and close the two intake valves 7 in the third cylinder. Two intake cams 51 arranged above two intake valves 7 arranged in the fourth cylinder simultaneously open and close the two intake valves 7 in the fourth cylinder.

[0019] The exhaust camshaft 6 is provided with a plurality of exhaust cams 61 spaced apart from one another in the axial direction of the exhaust camshaft 6. In this embodiment, eight exhaust cams 61 are provided on the exhaust camshaft 6 to open and close a total of eight exhaust valves 8 arranged in four cylinders. The two exhaust cams 61 arranged above the two exhaust valves 8 arranged in the first cylinder simultaneously open and close the two exhaust valves 8 in the first cylinder. The two exhaust cams 61 arranged above the two exhaust valves 8 arranged in the second cylinder simultaneously open and close the two exhaust valves 8 in the second cylinder. The two exhaust cams 61 arranged above the two exhaust valves 8 arranged in the third cylinder simultaneously open and close the two exhaust valves 8 in the third cylinder. The two exhaust cams 61 arranged above the two exhaust valves 8 arranged in the fourth cylinder simultaneously open and close the two exhaust valves 8 in the fourth cylinder.

[0020] As described above, in this embodiment, the internal combustion engine 1 is provided with a camshaft on each of the intake valve side and the exhaust valve side. That is, the internal combustion engine 1 is a so-called DOHC (Double Over Head Camshaft) internal combustion engine. The valve train on the intake valve side will be described in detail below, but the valve train on the exhaust valve side has the same configuration as the valve train on the intake valve side. That is, the exhaust camshaft 6 has the same configuration as the intake camshaft 5.

[0021] 2 is a schematic partial cross-sectional view of the internal combustion engine 1. FIG. 2 shows a cross-sectional view of the periphery of the intake valve 7. The internal combustion engine 1 is equipped with a valve train that drives the intake valve 7. The valve train has an intake camshaft 5, a valve lifter 14, and a valve spring 15. In this embodiment, the valve train is a direct-hit (direct-acting) valve train configured so that an intake cam 51 of the intake camshaft 5 directly presses the valve lifter 14.

[0022] The valve lifter 14 has a cylindrical shape and is slidable along a guide hole 161 formed in the cylinder head 16. The end of the valve stem 71 of the intake valve 7 abuts against the inner surface of the valve lifter 14. A spring retainer 18 is attached to the end of the valve stem 71 by a cotter 17. The valve spring 15 extends in the axial direction of the valve stem 71 between the spring retainer 18 and a spring seat 19.

[0023] The valve stem 71 is slidably supported by the valve guide 20. The valve spring 15 biases the intake valve 7 toward the intake camshaft 5. As a result, the valve head 72 of the intake valve 7 closes the end of the intake port 21 that communicates with the intake passage.

[0024] The intake cam 51 is fixed to a shaft portion 52 of the intake camshaft 5 and converts the rotational motion of the intake camshaft 5 into linear motion of the intake valve 7. When the intake cam 51 comes into contact with the valve lifter 14 due to the rotation of the intake camshaft 5, the rotational force of the intake camshaft 5 is transmitted to the valve lifter 14 via the intake cam 51. As a result, the valve lifter 14 and the intake valve 7 move linearly away from the intake camshaft 5, and the valve head 72 opens the end of the intake port 21. Therefore, the intake camshaft 5 rotates in accordance with the rotation of the crankshaft 4, thereby opening and closing the intake valve 7.

[0025] Figure 3 is a timing chart showing the valve lift of the intake valve and the cam torque generated on the intake camshaft. Figure 3 shows data related to the intake cam of the first cylinder (#1) and data related to the intake cam of the third cylinder (#3) next to the first cylinder for a comparative example (broken line) based on the prior art and an example (solid line) based on this embodiment. The change in valve lift over time is called a lift curve.

[0026] When the intake cam opens the intake valve, positive cam torque is generated on the intake camshaft, and when the intake cam closes the intake valve, negative cam torque is generated on the intake camshaft. Positive cam torque peaks between the valve opening position, where the intake valve starts to open, and the maximum lift position, where the intake valve lift is at its maximum. On the other hand, negative cam torque peaks between the maximum lift position and the valve closing position, where the intake valve is completely closed. Note that positive cam torque refers to the torque required to rotate the camshaft, and negative cam torque refers to the torque that promotes the rotation of the camshaft.

[0027] In the example shown in FIG. 3, the timing at which the intake valve 7 of the third cylinder begins to open is slightly earlier than the timing at which the intake valve 7 of the first cylinder completes closing. As shown in FIG. 3, the intake cam of the comparative example has a symmetric lift curve in which the maximum lift position (crank angle A1) is located midway between the valve opening start position and the valve closing completion position. The negative cam torque generated by the intake cam of the first cylinder peaks at a timing (crank angle A3) before the positive cam torque is generated by the intake cam of the third cylinder. In this case, torque fluctuations of the intake camshaft increase because the negative cam torque is not offset by the positive cam torque at the peak position of the negative cam torque. This results in increased flutter and reduced durability of transmission devices such as timing chains.

[0028] On the other hand, the intake cam of the embodiment has an asymmetric lift curve in which the maximum lift position (crank angle A2) is closer to the valve-closing completion position than the valve-opening start position, and the negative cam torque generated by the intake cam of cylinder No. 1 reaches its peak when the positive cam torque is generated by the intake cam of cylinder No. 3 (crank angle A4). In this case, the negative cam torque is offset by the positive cam torque at the peak position of the negative cam torque, resulting in smaller torque fluctuations in the intake camshaft compared to the comparative example.

[0029] That is, in this embodiment, the multiple intake cams 51 have asymmetric lift curves in which the maximum lift position is closer to the valve closing position than the valve opening start position, and are configured so that the peak position of the negative cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 arranged in the first cylinder is included in the phase section in which the positive cam torque is generated by the second intake cam 51 that opens and closes the intake valve 7 arranged in the second cylinder. This makes it possible to reduce the peak value (absolute value) of the negative cam torque. Therefore, with the intake camshaft 5 according to this embodiment, torque fluctuations of the intake camshaft 5 can be suppressed while ensuring the degree of freedom in valve opening and closing control.

[0030] In this embodiment, the multiple intake cams 51 have the following cam profile in order to obtain the above-described lift curve. Figure 4 is a diagram showing an example of the cam profile of the intake cam 51. In this embodiment, the multiple intake cams 51 provided on the intake camshaft 5 have the same cam profile.

[0031] 4, intake cam 51 has valve-opening side buffer section 51a, valve-opening side lift section 51b, valve-closing side lift section 51c, and valve-closing side buffer section 51d. Valve-opening side buffer section 51a and valve-opening side lift section 51b are located on the valve-opening side (forward in the rotational direction) of nose top T, which corresponds to the maximum lift position, and form a valve-opening side section that contributes to opening of intake valve 7. On the other hand, valve-closing side lift section 51c and valve-closing side buffer section 51d are located on the valve-closing side (backward in the rotational direction) of nose top T and form a valve-closing side section that contributes to closing of intake valve 7. Valve-opening side buffer section 51a has a rotation angle θa, valve-opening side lift section 51b has a rotation angle θb, valve-closing side lift section 51c has a rotation angle θc, and valve-closing side buffer section 51d has a rotation angle θd.

[0032] The intake cam 51 is configured so that the sum of the rotation angles θa and θb is greater than the sum of the rotation angles θc and θd. In other words, the intake cam 51 is configured so that its valve-opening side section is longer than its valve-closing side section. Therefore, the crank angle from the valve-opening start position to the maximum lift position is longer than the crank angle from the maximum lift position to the valve-closing end position, and the maximum lift position is biased toward the valve-closing side. Therefore, the intake cam 51 having such a cam profile achieves an asymmetric lift curve in which the maximum lift position is closer to the valve-closing end position than the valve-opening start position. Furthermore, the phases of the multiple intake cams 51 on the intake camshaft 5 are set so that the peak position of the negative cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 of the first cylinder is included in the phase section in which the positive cam torque is generated by the second intake cam 51 that opens and closes the intake valve 7 of the second cylinder.

[0033] Fig. 5 is a diagram showing the change over time in cam torque generated by multiple intake cams 51 having the cam profile shown in Fig. 4. In Fig. 5, the cam torque generated by the intake cams 51 of the first cylinder (#1) to the fourth cylinder (#4) is shown by a dashed line, and the composite cam torque generated on the intake camshaft 5 by these intake cams 51 is shown by a solid line. For reference, Fig. 5 also shows the waveform of the lift curve obtained by the intake cam 51 of the first cylinder by a dashed line.

[0034] In the data of Figure 5, the peak position of the negative cam torque generated by the intake cam 51 of cylinder 1 approximately coincides with the peak position of the positive cam torque generated by the intake cam 51 of cylinder 3, the peak position of the negative cam torque generated by the intake cam 51 of cylinder 3 approximately coincides with the peak position of the positive cam torque generated by the intake cam 51 of cylinder 4, the peak position of the negative cam torque generated by the intake cam 51 of cylinder 4 approximately coincides with the peak position of the positive cam torque generated by the intake cam 51 of cylinder 2, and the peak position of the negative cam torque generated by the intake cam 51 of cylinder 2 approximately coincides with the peak position of the positive cam torque generated by the intake cam 51 of cylinder 1. That is, the multiple intake cams 51 are formed so that the peak position of the negative cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 arranged in the first cylinder (e.g., cylinder 1, 3, 4, or 2) substantially coincides with the peak position of the positive cam torque generated by the second intake cam 51 that opens and closes the intake valve 7 arranged in the second cylinder (e.g., cylinder 3, 4, 2, or 1). This makes it possible to reduce not only the peak value of the negative cam torque but also the peak value of the positive cam torque, thereby further suppressing torque fluctuations in the intake camshaft 5. Note that, in this specification, "substantially coincident" between the peak position of the negative cam torque and the peak position of the positive cam torque means that the difference between the peak positions is 10° or less.

[0035] The intake cams 51 may have asymmetric lift curves in which the maximum lift position is closer to the valve-opening start position than the valve-closing completion position, and the peak position of the positive cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 arranged for the first cylinder may be included in the phase interval in which the negative cam torque is generated by the second intake cam 51 that opens and closes the intake valve 7 arranged for the second cylinder. This reduces the peak value of the positive cam torque. Therefore, even with this modification, torque fluctuations of the intake camshaft 5 can be suppressed while ensuring the degree of freedom in valve opening and closing control. In this case, for example, the intake cam 51 is formed so that the valve-closing side interval is longer than the valve-opening side interval. That is, in the cam profile shown in FIG. 4, the sum of the rotation angles θc and θd is greater than the sum of the rotation angles θa and θb.

[0036] Furthermore, the intake cams 51 may have asymmetric lift curves in which the maximum lift position is closer to the valve opening start position than the valve closing completion position, and may be formed so that the peak position of the positive cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 arranged in the first cylinder substantially coincides with the peak position of the negative cam torque generated by the second intake cam 51 that opens and closes the intake valve 7 arranged in the second cylinder. This makes it possible to further suppress torque fluctuations in the intake camshaft 5.

[0037] In addition, when the maximum lift position is closer to the valve closing completion position than the valve opening start position, the valve opening speed can be slower than when the maximum lift position is closer to the valve opening start position than the valve closing completion position. Therefore, in the former case, deviation of the actual opening and closing operation of the intake valve 7 from the designed lift curve can be suppressed more effectively than in the latter case, thereby improving the stability of the opening and closing control of the intake valve 7.

[0038] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments and various modifications and changes can be made within the scope of the claims. For example, one intake valve 7 and one exhaust valve 8 may be provided for each cylinder.

[0039] The valve mechanism used to open and close the intake valve 7 and the exhaust valve 8 may be a rocker arm type valve mechanism in which a cam on a camshaft presses a valve lifter via a rocker arm. The internal combustion engine 1 may also be an SOHC (Single Over Head Camshaft) type internal combustion engine in which the intake valve 7 and the exhaust valve 8 are opened and closed by a single camshaft. [Explanation of symbols]

[0040] 1. Internal combustion engine 4 crankshaft 5. Intake camshaft 51 Intake cam 6 exhaust camshaft 61 Exhaust cam 7 Intake valve 8 Exhaust valve 10 Intake timing sprocket 11 Exhaust timing sprocket 12 Timing chain 13 Timing sprocket

Claims

[Claim 1] 1. A camshaft in an internal combustion engine that is rotationally driven by a crankshaft via a transmission, a plurality of cams spaced apart from one another in the axial direction of the camshaft; The camshaft has asymmetric lift curves, and the cams are formed so that a peak position of negative cam torque generated by a first cam that opens and closes a valve disposed in a first cylinder substantially coincides with a peak position of positive cam torque generated by a second cam that opens and closes a valve disposed in a second cylinder.

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